1. Field of the Invention
The invention generally relates to handling an attach procedure, and more particularly, to apparatuses and methods for handling an attach procedure in a mobile communication system environment.
2. Description of the Related Art
In a typical mobile communication system environment, a mobile user equipment (UE) communicates with one or more mobile communication systems via the radio access networks of the mobile communication systems. A UE comprises various types of equipment such as a mobile telephone (also known as cellular or cell phone), a laptop with wireless communication capability, a personal digital assistant (PDA) etc. The equipment may be portable, handheld, pocket-sized, and installed in a vehicle etc and communicate voice and/or data signals with the radio access network.
A universal mobile telecommunications system (UMTS) is a third generation mobile communication system that has evolved from the Global System for Mobile communications (GSM) system. The UMTS is a European standard which aims to provide better mobile communication services based on the GSM core network and wideband code division multiple access (W-CDMA) technology. Although UMTS delivers high data transfer rates, wireless data usage is expected to increase significantly over the next few years. For this reason, concepts for UMTS Long Term Evolution (LTE) have been proposed and the objective is to further improve UMTS to achieve high-data-rates, low-latency and packet-optimized radio access technology. The improved UMTS technology is called Evolved Universal Terrestrial Radio Access (E-UTRA) and the system employing the E-UTRA technology is called an Evolved Packet System (EPS).
For a UE, which complies with the 3GPP specifications for the E-UTRA protocol, the 3GPP TS 24.301 specification, v.1.0.0, referred to herein as the 24.301 specification, addresses the subject of the Non-Access-Stratum (NAS) protocol requirements for the EPS and the UE.
After the UE is powered on and connects to the EPS, it will need to perform an attach procedure to register itself to the EPS so that it can start a packet data session over the EPS. As illustrated in FIG. 1, the attach procedure starts by the UE sending an ATTACH REQUEST message to the EPS (step S101). The ATTACH REQUEST message may be sent combined with a PDN CONNECTIVITY REQUEST message indicating that the UE wishes to start a packet data session with the EPS. When the EPS receives the ATTACH REQUEST message, it authenticates the UE, checks if the UE is authorized to have access to packet data services, and performs a security mode control procedure to activate the encryption on subsequent messages (step S102). If none of the checks fails, the EPS accepts the attach request by sending an ATTACH ACCEPT message to the UE. The ATTACH ACCEPT message may be sent combined with an ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message if the PDN CONNECTIVITY REQUEST message is found in the ATTACH REQUEST message (step S103). The ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message contains the configuration used to activate the default bearer for the packet data session. When the UE receives the ATTACH ACCEPT message, it checks the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message to see if the configuration within is acceptable. If the UE accepts the configuration specified in the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message, it applies the configuration, resets the counters associated with the attach procedure, including the attach attempt counter and the tracking area updating attempt counter, enters the EMM-REGISTERED state, and sets the EPS update status to EU1 UPDATED (step S104). The UE then responds to the EPS with an ATTACH COMPLETE message to acknowledge that it has received and accepted the ATTACH ACCEPT message (step S105). The ATTACH COMPLETE message may be sent combined with an ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT message indicating that the UE has accepted the configuration of the default bearer from the ACTIVATE DEFAULT EPS BEARER CONTEXT REQUEST message. At last, the EPS receives the ATTACH COMPLETE message combined with the ACTIVATE DEFAULT EPS BEARER CONTEXT ACCEPT message and the attach procedure ends successfully.